The present invention relates to a DC power supply and more particularly to such a power supply which is adapted to be energized from AC supply mains and to accommodate a wide range of AC supply voltage.
Increasingly, DC power supplies for computers and other electronic systems operated from AC supply mains employ a relatively high frequency DC to DC switching inverter. A filter capacitor or other energy storage device is normally provided at the input terminals of the inverter so as to provide a source of current during those portions of the AC supply cycle when the instantaneous voltage is below that necessary to operate the inverter. However, when the power supply is required to operate over a wide range of AC input voltages, the system components and particularly the energy storage element, must be sized and rated to accommodate the maximum input voltage. For example, if the system must accommodate input voltages ranging from 90 volts AC to 270 volts AC the voltage rating of the components must be essentially three times the values which would just operate the system at the minimum voltage. Further, since power and energy stored go as the square of the voltage, the required size of the components, especially the input energy storage device, will go up essentially by a factor of nine.
In accordance with the practice of the present invention, the cost of this over capacity is avoided by interposing a semi-conductor switching device between the AC supply mains and the energy storage device, e.g., the filter capacitor, and by operating the switching device in response to the applied voltage so that the storage device is disconnected from the supply mains whenever the voltage supplied to the storage element exceeds a pre-selected level.